In the prior art, there is a known high speed and high load cylinder device applicable for a press machine, such as a turret punch press and so forth, a machine tool and so forth, which is illustrated in FIG. 1, for example.
The above-mentioned cylinder device is constructed by connecting a piston of a high speed cylinder a, to be operated at high speed, and a piston of a pressurizing cylinder b bearing a high load, via a piston rod, and by communicating upper and lower chambers of the pressurizing cylinder b via an externally provided piping d and a valve c provided in the piping. Upon high speed operation, the upper and lower chambers of the pressurizing cylinder b communicate by opening the valve c so that a pressure difference is not caused even when a hydraulic pressure is supplied from a hydraulic circuit f to enable high speed operation of the high speed cylinder. Upon generating a large pressure force, the valve c is closed so that a pressure difference may be generated between the upper and lower chambers of the pressurizing cylinder b so as to cope with high load by the pressurizing cylinder b. It should be noted that, in FIG. 1, g denotes a hydraulic pump, h denotes a switching valve and i denotes a tank.
However, since the above-mentioned conventional cylinder device is provided externally of the valve c and the piping d, the stroke of the pressurizing cylinder b becomes long so as to expand the length of piping d in association therewith. This causes a problem of creating a high fluid path resistance during high speed operation when a large amount of a working fluid at one time is to be fed.
Also, for permitting flow of a large amount of the working fluid, a large diameter piping and large size valve c become necessary to make the device per se costly. Furthermore, since the construction becomes complicated, it may cause leakage.
The present invention is worked out for improving such defects in the prior art. It is an object of the present invention to provide a high speed and high load cylinder device which enables operation corresponding to high speed operation and high load operation without requiring an external piping.